The invention relates to apparatus and methods for treating malignant tissue known as "cancer eye" in the eyes of livestock by applying high frequency current, by means of spaced probes, to the malignant tissue to increase the temperature thereof to a level which is high enough to kill the malignant tissue but is low enough to avoid permanent damage to the adjacent healthy tissue.
Benign and malignant tumors of the eye and eyelid in cattle are generally referred to by the term "cancer eye". Approximately 80% of such tumors are malignant and many of the rest become malignant with time. Cancer eye is a serious problem throughout the United States, especially in high elevation locations where solar radiation is most intense. As pointed out by his article "Electrothermal treatment of Cancer Eye" by James D. Doss, published in the August 1977 issue of the LASL Mini-Review, 77-14, published in 1975 by the Los Alamos Scientific Laboratory of the University of California at Los Alamos, N. Mex., cancer eye was the leading individual cause of cattle carcass condemnation at slaughter houses inspected by the United States Department of Agriculture. In that year, losses due to cancer eye were though to exceed $20,000,000.00 per year in the United States alone. As a result of research at the above-mentioned Los Alamos Scientific Laboratory, techniques have been developed for on-range use involving passage of high frequency current through malignant tissue to increase its temperature to approximately 50.degree. C. (122.degree. F.) for thirty seconds, resulting in effective arresting of early discovered cases of cancer eye in cattle. Such temperature preferentially kills cancer cells, which are usually more susceptible to permanent damage by heat than healthy cells.
Several hand-held electrothermal devices have been developed which include high frequency oscillators that produce the needed high frequency current thorugh closely spaced probes that are pressed sufficiently hard against the malignant tissue to ensure good electrical contact thereto. In usual practice, the treatment of an animal with cancer eye involves the steps of restraining the animal, placing an eye spoon underneath and behind the eye ball to elevate and immobilize the eyeball. The electrodes of the electrothermal device then are held firmly against the surface of the tumor. The oscillator is activated, and high frequency current flows through the probes and the tissue and raises the temperature of the tissue, which in turn raises the temperature of the probe. When the temperature of the probe tip reaches the minimum required 50.degree. C. temperature, the instrument emits periodic audible beeps every second, allowing the user to measure the amount of time adequate pressure of the electrodes is maintained against the surface of the tumor (for 30 seconds) by counting thirty beeps. A device manufactured by Veterinary Products Industries, of Phoenix, Ariz., referred to as the THERM.multidot.I.multidot.CURER LCF (localized current field) electronic probe, has been developed based on the above-mentioned research. This device produces an initial heat surge to a temperature of about 160.degree. F. (60.degree. C.) to 180.degree. F. (68.degree. C.) and then drops back to the sustained temperature of 50.degree. C. for the required 30 second treatment. This initial surge is supposed to have a cauterizing effect that stops any bleeding, but, in fact, can cause undue permanent damage to healthy eye tissue.
The previous electrothermal devices and treatments, while representing a breakthrough in the treatment of cancer eye in cattle, nevertheless present certain unsolved problems. For example, the animal being treated usually vigorously resists attempts to restrain it, causing difficulty to the veterinary in maintaining adequate contact of the current probe contact surfaces with the tumorous tissue. But if adequate continuous electrical contact is not maintained during the entire treatment period, the temperature of the tissue may not reach or maintain the necessary temperature of 50.degree. C. One of the previous electrothermal devices dissipates far too much power in the circuitry located in the handle of the device. Since it is frequently desirable to use the device at locations where electrical power is not available, it is highly desirable that the electrothermal devices be lightweight and battery-powered. This, of course, leads to the requirement that the electrothermal device not dissipate and waste excessive power. Another problem that sometimes occurs with prior art electrothermal devices is that the initial surge of current actually heats up tissue so rapidly that the temperature increase of the sensor (usually a thermistor) located in one of the probe tips lags the tissue temperature so that the circuitry cannot adequately regulate the amount of high frequency current applied to the tumor tissue before overheating of the tissue occurs. Such overheating can permanently damage healthy tissue which, of course, is highly undesirable.
Thus, there is an unmet need for an improved apparatus and method for electrothermal treatment of cancer eye in livestock. More specifically, there is a need for an improved electrothermal device and method which makes it easier for a veterinary to maintain sufficient pressure of the current probe contact surfaces against the cancer eye tissue to ensure adequate heating thereof despite any struggling by the animal.
There also is a need to provide such an electrothermal device and method that avoids excessive dissipation and waste of power.
There also is a need for such an electrothermal device that avoids excessive initial temperature overshoot or overheating of the cancer eye tissue.
Therefore, it is an object of the invention to provide an improved apparatus and method for electrothermal treatment of cancer eye or other tumorous tissue wherein a veterinary or other user is immediately and reliably alerted as to whether or not adequate pressure of the contact area of the current probes is being maintained against the cancer eye tissue or tumorous tissue.
It is another object of the invention to provide an apparatus and method for electrothermal treatment of cancer eye wherein the amount of wasted power dissipation is minimized.
It is another object of the invention to provide an apparatus and method for electrothermal treatment of cancer eye wherein the temperature of the cancer eye tissue is accurately maintained within a predetermined range during the treatment procedure.
It is another object of the invention to provide a device for electrothermal treatment of cancer eye wherein excessively rapid initial build-up of temperature in the cancer eye tissue is automatically avoided.